Microbial Energy Conversion: The Proceedings of a Seminar Sponsored by the UN Institute for Training and Research (UNITAR) and the Ministry for Research and Technology of the Federal Republic of Germany Held in Göttingen, October 1976

Microbial Energy Conversion documents the proceedings of a seminar in Gottingen in October 1976. This book discusses the potential of microorganisms to use solar energy or convert biomass produced by solar energy in such a way that new microbial energy sources can supplement or partially replace conventional sources. This compilation reviews biomass production and elaborates on in detail the microbial processes that are involved in the conversion of the primary biomass—either freshly harvested or disposed of as waste—into energy sources that are similar to hydrogen, methane, propane, gasoline, Diesel oil, methanol, ethanol, or electricity. The microbial processes that contribute to the development of known energy resources, such as mining of low grade ores of copper, zinc, and uranium; reclamation of oil from oil shale; and recovery of conventional and heavy oil and gas, are also deliberated. This text likewise elaborates on the study of photosynthetic enzyme systems, hydrogenase, immobilization of enzymes and pigments on membranes, and construction of artificial photosynthetic units. This book is beneficial to students and researchers conducting work on microbial energy conversion.

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 22, 2013
• ISBN: 9781483139128

Book preview

Schlegel

INTRODUCTION TO RECOMMENDATIONS

RECOMMENDATIONS

made by the Working Groups

with respect to further research in the field of microbial energy conversion

The members of the Working Groups are listed on page

WORKING GROUP I

Biomass

Publisher Summary

At present, about 98% of the energy that is used by mankind is derived from biomass including fossil fuels. About 2 % of the energy is derived from other sources. This chapter discusses various methods for conversion and utilization of biomass. Basic and applied research in the mechanisms of photosynthesis could be material to fully utilize photosynthetic potential of biomass. The use of the biomass produced should be optimized by conversion to food and feed, fibre and chemicals, and fuel. In contrast to primary protein-poor biomass microbial high–quality biomass—yeasts, bacteria—rich in protein can be produced with very high yields per unit of volume. The technology development could also lower the still high production costs of biomass. The microbial biomass should be produced by refinement of cheap organic and inorganic wastes. It is desirable to make more use of the 1.7 × 10¹¹ tons of biomass produced annually in an ecologically sound manner.

At the present time about 98 % of the energy used by mankind is derived from biomass including fossil fuels. About 2 % is derived from other sources. Therefore, the following recommendations are made:

1. It is desirable to make more use of the 1.7 × 10¹¹ tons of biomass produced annually in an ecologically sound manner. Only about 1 % is currently used for fuel and fibre and about 1 % for food and feed.

2. The rest (98 %) is not used due mainly to the high cost of harvest and transport. These costs might be substantially lowered if biomass were converted at its site of production into easily transportable products. It is also desirable to concentrate biomass production in time and space according to local opportunities.

3. Better methods for conversion and utilization should be developed.

4. Basic and applied research in the mechanisms of photosynthesis could be material to fully utilize photosynthetic potential.

5. Use of the biomass produced should be optimized by conversion to:

a) food and feed

b) fibre and chemicals

c) fuel.

6. In contrast to primary protein-poor biomass microbial high quality biomass (yeasts, bacteria) rich in protein can be produced with very high yields per unit of volume. Technology development might lower the still high production costs. Microbial biomass should be produced by refinement of cheap organic and inorganic wastes.

WORKING GROUP II

Recycling of Wastes

Publisher Summary

This chapter discusses recycling of wastes. Microbial processes play a major role in waste treatment, purification, and disposal whether in natural cycles or in man-made waste handling technology. Such processes and development of new ones can be effectively used in recycling of wastes into valuable by-products and energy. Waste material such as municipal liquid wastes (sewage), municipal solid wastes (garbage), industrial organic wastes, agricultural liquid and solid wastes (vegetable and animal wastes), and carbon di oxide and heat wastes of power plants are produced in the world at quantities of billions of tons per year and contain energy, nitrogen, and other valuable substrates. This chapter discusses various biological processes such as aerobic microbial processes, which contain aerobic processes of agricultural wastes and composting of municipal solid wastes, photosynthetic algal processes, photosynthetic bacterial processes, and anaerobic fermentation to products other than methane. The economic benefit of recycling of waste matter and the recovery of valuable byproducts also include the economic value of the betterment of the environment. The future of waste microbial recycling depends to a great extent on better waste handling management by the waste producer.

Microbial processes play a major role in waste treatment, purification and disposal whether in natural cycles or in man-made waste handling technology. Such processes and development of new ones can be effectively used in recycling of wastes into valuable byproducts and energy. In this context the Working Group II excluded from its discussions methane production from wastes (covered by Working Group III) and biological processes aimed primarily at the treatment and degradation of wastes for the protection of the environment and recycling of water. The direct conversion of wastes into animal food has also been excluded.

The following sources of wastes were considered:

A Municipal liquid wastes (sewage)

B Municipal solid wastes (garbage)

C Industrial organic wastes

D Agricultural liquid and solid wastes (vegetable and animal wastes)

E CO2 and heat wastes of power plants

Such waste materials are produced in the world at quantities of billions of tons per year and contain energy, nitrogen and other valuable substrates.

The following recommendations were adopted with regard to the various biological processes:

1 Aerobic Microbial Processes

A Aerobic processes of liquid wastes

Biomass from processes such as activated sludge of municipal wastes and of industrial wastes (for example yeast production on sulfite-liquors in the paper industry and dairy wastes) should be considered as a possible proteinaceous food for animals or as a source of fertilizers. Research should be centered on methods of dewatering and processing of such sludges as well as on their nutritive value including hygienic and toxicological aspects.

B Aerobic processes of agricultural wastes

Aerobic fermentation of animal wastes with the possibility of thermophilic microbial processes should be further developed aiming at the utilization of the biomass and product material as a source of animal feeding or as a source of material for biomass production (yeast, algae), from which valuable substances (e.g. vitamins, enzymes, biochemicals) can be obtained. Design parameters and intensification of such processes are still to be developed.

Microbial degradation of cellulosic and hemicellulosic material to produce proteinaceous biomass and other byproducts should be encouraged due to the vast mass of material produced (for example bagasse). Improving transportation problems, screening of microorganisms and development of process parameters are needed.

C Composting of municipal solid wastes

Combined compostation of municipal solid wastes together with sewage sludges should be further developed due to the thermophilic destruction of pathogenes. Development of technologies to increase the value of compost final product (for example to produce insulation boards or food) are needed due to the diminishing demand of compost in developed countries. The value of compost as a source of fertilizers in developing countries should be emphasized with the development of letter techniques.

2 Photosynthetic Algal Processes

Algal production or liquid municipal, agricultural and organic industrial wastes are to be encouraged in regions of ample sunlight as a source of proteins to animals and as a source of oxygen for waste degradation. Fermentation of algal biomass (methane, ethanol, hydrogen etc.) and its value as a fertilizer are also to be investigated.

Improving system efficiency in order to reduce area requirements, improving algal dewatering, drying and processing techniques, selective cultivation of desirable species and extensive feeding experiments with various animals require further efforts of research and development.

Special emphasis should be given on the development of algal processes in rural areas of developing countries, using domestic and animal wastes, possibly with combination of anaerobic methanogenic fermentation to produce proteins. Wet feeding of algae to animals and fish should be preferred in such regions.

3 Photosynthetic Bacterial Processes

Due to their effectiveness in the treatment of concentrated organic wastes, their high light conversion efficiency and efficient biomass production, photosynthetic bacterial processes (both aerobic and anaerobic) should be further developed.

Process optimization of separation of the biomass and its use as single cell proteins for feeding of animals (poultry, fish etc.) or as a source of fertilizers are to be vigorously further investigated.

4 Anaerobic Fermentation to Products other than Methane

Anaerobic digestion of organic wastes produces valuable fatty acids. Priority should be given to the development of processes, whereby fatty acids can be extracted and utilized, while the biomass can serve for animal food purposes or fertilizer and the residual waste substrate would be further treated (by algal, photosynthetic bacterial, or other methods). Anaerobic microbial production of substances which can already be prepared (e.g. ethanol, acetone, ethylene glycol, isopropanol) should be supported. New substances, which cannot be prepared by simple chemical methods, should be prepared by waste fermentations.

It should be noted that the economic benefit of recycling of waste matter and the recovery of valuable byproducts should also include the economic value of the embetterment of the environment accomplished by using a given process.

The future of waste microbial recycling depends to a great extent on better waste handling management by the waste producer. Special emphasis should be made on source control of toxic and hazardous materials and segregation of non-recoverable wastes from recoverable ones, minimizing excess dilution of wastes. The use of excess powerplant heat to enhance biological processes and CO2 as an algal carbon source are examples of proper resource recovery management.

A major effort should be made in motivating the public to use recycled material. The development of faster and more reliable toxicological tests of recycled byproducts, especially for animal food, are required.

The recommendations of this working group concern many different microbial processes. Therefore, it was not possible to treat each individual process in detail (e.g. as compared with the methane production process of Working Group III).

WORKING GROUP III

Methane Production

Publisher Summary

This chapter discusses the production of methane by fermentation of organic material, which offers the potential for production of significant quantities of fuel gas. This fuel gas can supply a small portion of the present energy needs of industrialized economies and a significant portion in some non-industrial economies. However, several technical problems should be solved before conditions become favorable for widespread use of this energy. A major factor in determining the economics of methane production is the efficiency with which the microorganisms convert the substrate to methane. This efficiency is dependent upon many factors including plant species, growth stages, and soil properties. At present, there is no standardized method for determining the substrate biodegradability. The substrate biodegradability can be enhanced with certain pretreatment processes such as thermal, thermo-chemical, and size reduction. The certain characteristics of potential substrates such as the metal, glass, and ash content of urban refuse can cause significant operational problems in the processing system.

The production of methane by fermentation of organic material offers the potential for production of significant quantities of fuel gas. This fuel gas may supply a small portion of the present energy needs of industrialized economies and a significant portion in some non-industrial economies. However, several technical problems must be solved before conditions will be favorable for wide spread use of this energy. In addition to these technical problems, questions relating to the variety of possibilities for resource allocation and the economics of the installation of processing plants at specific locations must be answered. Because of the variety and complexity of these questions, recommendations of universal applicability can not be formulated. Also specific cultural and societal characteristics materially influence the feasibility of controlled methanogenesis. Therefore, only recommendations relating to technical matters can be advantageously formulated at this seminar. These recommendations have application to all countries.

Because of the vast quantities of fuel gas required, it is necessary to be able to obtain large quantities of suitable organic substrates in order for the contribution from methanogenesis to be significant. Therefore, it is recommended to:

1. Survey the available organic substrates identifying location and collection problems as well as competitive uses for these materials.

A major factor in determining the economics of methane production is the efficiency with which the microorganisms convert the substrate to methane. This efficiency is dependent upon many factors including plant species, growth stages and soil properties. At present there is no standardized method for determining the substrate biodegradability. It is, therefore, recommended to:

2. Develop a rapid controlled standardized technique for assessment of the biodegradability of specific substrates to methane.

Substrate biodegradability can be enhanced with certain pretreatment processes such as thermal, thermo-chemical and size reduction. At present it appears that the pretreatment may be costly and energy intensive. It is recommended to:

3. Continue studies of pretreatment processes for increasing biodegradability and ascertain the feasibility of selected methods based on the needs of specific locations.

Past work in plant genetics has been directed toward the production of food or plant fibers for specific industrial uses. Development of plants that have high dry matter yields with a low lignin content to make them more biodegradable could significantly improve the energy production from this process. It is recommended to:

4. Screen known plant species to determine those species that may be ideal candidate crops and initiate genetic manipulations to produce a super energy plant.

Certain characteristics of potential substrates such as the metal, glass and ash content of urban refuse may cause significant operational problems in the processing system. Therefore, it is recommended to:

5. Develop techniques for the storage and preparation of each substrate as required to minimize operation and maintenance problems.

Based on the research on methane fermentation during the past several decades, much is known regarding the optimum fermentation conditions. However, the effect of temperature on the reaction kinetics of the fermentation process appears to be substrate dependent. This effect is critical in the design of a successful fermentation system. Therefore, it is recommended to:

6. Develop data relating fermentation kinetics to fermentation temperatures for specific substrates.

One important characteristic of the methane fermentation process is the conservation of plant nutrients, especially nitrogen. Return of the residue from this process to the land adds both plant nutrients and organic material to the soil. Application of this residue to the land may present potential health hazards and environmental problems. It is recommended to:

7. Evaluate the potential health hazards and environmental problems associated with the disposal of the residue on land.

Other uses for this residue may be possible, especially the residual fibers. High costs are associated with the separation of the solids from the fermenter slurry. It is recommended to:

8. Evaluate the fermentor slurry characteristics and develop more efficient techniques for processing the residual slurry for utilization and for final disposal.

Mixing of the fermentation reactor is known to increase the rate of methane fermentation. However, the mixing intensity required and the relationship between mixing and reactor geometry have not been clearly defined. This is especially true for small low rate systems. It is recommended to:

9. Evaluate the degree of mixing required and develop a simple efficient mixing device for small fermentation systems.

There is presently a wealth of information regarding the methane fermentation and the design and operation of methane fermentation systems. Transfer of this information to scientists and engineers who expect to be working on these systems is necessary. It is, therefore, recommended to:

10. Establish training programs and documents for information transfer to countries as appropriate.

Discussion of gas utilization resulted in the conclusion that there are many potential uses for the gas produced by this system. Technology exists for processing the gas to any degree required. Costs may be substantial for gas purification and the value of the purified gas must justify the added expense. It was recognized that refinement or improvement of any processing step in the overall system may result in a lower cost of gas production. However, except as identified above, existing technology appears to be adequate for producing methane at a cost that may be acceptable. Complete evaluation of each processing parameter for this system was not possible during this seminar. Only those factors identified as major inhibitors in the application of this process are presented. It is recommended that funds be provided to support research and information transfer in these areas.

WORKING GROUP IV

Photoproduction of Hydrogen/Purple Membrane

Publisher Summary

The advantage of the single-stage biophotolysis is that water is a cheap available substrate. However, the disadvantages of the single stage biophotolysis include the inactivity of hydrogenase enzymes in the presence of oxygen, the instability of photosynthetic—quantum capture—apparatus, the poor light intensity characteristics of single stage biophotolysis, the inefficiency at high light intensities, the aqueous system being susceptible to biodegradation, and the autooxidizability of natural/artificial electron carriers. The advantages of hydrogen production through photosynthetic bacteria are the hydrogen production from organic substrates or inorganic substrates is easily demonstrable, the system is stable either as a cell suspension or after cell immobilization, and the hydrogen uses infrared light that is not used in conventional agriculture. The problems associated with hydrogen production through photosynthetic bacteria include the cost and availability of hydrogen donor and the need to assure absence of other contaminating organisms that can use hydrogen. However, hydrogen production through photosynthetic bacteria can be a very useful system for hydrogen production, provided alternate, cheap and abundant alternate hydrogen donors can be identified.

I Single stage biophotolysis:

Advantage:

Water is a cheap available substrate

Problems:

(a) Inactivity of hydrogenase enzymes in the presence of oxygen (>2 % oxygen).

(b) Instability of photosynthetic (quantum capture) apparatus.

(c) Poor light intensity characteristics; inefficient at high light intensities.

(d) Aqueous system will be susceptible to biodegradation (e.g., proteolysis, etc.).

(e) Autooxidizability of natural/artificial electron carriers.

Possible approaches:

(a) Screening program for organisms (preferably marine) which produce hydrogen at high rates for: (1) further study; and (2) as a source of hydrogenase.

(b) Focus on hydrogenase which exhibit little or no oxygen sensitivity during preparation and/or storage.

(c) Stabilization of hydrogenase and photocapture systems by chemical and/or physical means; i.e., immobilization, encapsulation, chemical fixation etc.

(d) Genetic approach to provide more (oxygen) stable hydrogenase and photocapture system.

(e.) Attempt to modify physiologically the photocapture system.

Conclusion and recommendations:

The process is still in the realm of basic research with no possibility for a functional system before the year 2000 and only then if research support is made available now.

Alternatives for photosynthetic system:

(a) Could be used for the preparation of ATP.

(b) To provide carbon compounds of use in other processes or as a source of hydrogen using a two-stage system.

II Hydrogen production - photosynthetic bacteria

Advantage:

(a) Hydrogen production from organic substrates (or inorganic substrates) is easily demonstrable.

(b) System is stable either as a cell suspension or after cell immobilization.

(c) Uses infra-red light not used in conventional agriculture.

Problems:

(a) Cost (and availability) of hydrogen donor.

(b) Need to assure absence of other contaminating organisms which may use H2.

Approaches and conclusions:

Can be a very useful system for hydrogen production provided alternate, cheap and abundant alternate hydrogen donors can be identified. Must also support a screening program to identify other organisms which can use efficiently the alternate hydrogen donor.

III H2-formation from organic matter by bacteria in the dark

(a) Applicability as a means of energy production

The efficiency of energy conversion by means of H2-formation from organic matter in the dark is at most 20 %. This is to be compared with an efficiency of 85 % in CH4-formation. Therefore, research in this area should concentrate on CH4-formation as a combustible endproduct rather than on H2-formation.

(b) Importance of H2 as an intermediate in CH4-formation and as a byproduct

CH4-formation from organic matter is known to involve H2, acetate, and CO2 as intermediates. Moreover, H2-formation as an intermediate has been shown to be the limiting step in CH4-formation from CO2. In order to be able to optimize CH4-formation it is, therefore, necessary to understand the regulation and properties of the H2-forming sytem.

H2-forming bacteria are also involved in the formation of organic compounds of considerable economic interest (e.g. acetone - butanol fermentation). The amount of H2 formed and of the other products excreted are directly interconnected. Research on the development and the optimization of fermentations in which H2 plus economical interesting compounds are formed should, therefore, be encouraged.

(c) The importance of research on hydrogenase

The formation of H2 as an intermediate involved hydrogenase as does light driven H2-formation. The mechanism and properties of the hydrogenase are still not understood and the enzyme is extremely difficult to handle. The understanding of the hydrogenase system from chemotrophic bacteria well, therefore, contribute to the understanding and handling of light driven H2-formation as an energy generating process.

IV Purple membrane

Advantages:

(a) Hypothetical production of current, ATP, O2, H2, or construction of an ion exchanger.

(b) Stable at pH 1 – 10, against O2, light, polymerizing agents etc.

(c) Relatively stable against biodegradation especially when operated in high salt concentration.

(d) Easy preparation of (1) bacteria; (2) purple membrane.

(e) Large theoretical areas of purple membranes can be achieved.

Disadvantages:

(a) Still in the stage of basic research.

(b) All demonstrated photoeffects are very poor.

(c) Transformation into large scale process cannot be discussed yet.

Summary:

(a) Model system for membrane function: (1) in intact cells; (2) in artificial systems.

(b) Due to its simplicity and stability very suitable for basic biotechnological research.

(c) But no technical use can be expected in the near future.

WORKING GROUP V

Microbial Recovery of Hydrocarbons

Publisher Summary

This chapter explores microbial recovery of hydrocarbons. Microbiology relates directly to the recovery and production of oil and gas from conventional reservoirs and tar sands, oil shale, and related sources. The enormous quantities of petroleum and gas consumed by the society and the increasing rate of consumption of fuels for energy purposes make exploration and development of additional and new approaches for conserving and recovering fossil fuel base essential. The utilization of microorganisms for specific bioconversion processes is amply documented. The degradation of paraffinic and aromatic hydrocarbons, the removal of complex detergents, waste management, antibiotic production, and fermentations of varied types, all represent examples of microbial processes that play a crucial role in today’s society. At present, petroleum microbiologists are few in number and not well organized. Therefore, the principal task is to structure the field of petroleum microbiology. A step forward in this direction is the establishment of an international microbiological centre. Such a centre can provide a focal point for the organization, coordination and cooperation of the research being done by the few petroleum microbiologists throughout the world.

Microbiology relates directly to the recovery and production of oil and gas from conventional reservoirs as well as tar sands, oil shale and related sources. Due to the enormous quantities of petroleum and gas consumed and considering the increasing rate of consumption for energy purposes, it becomes essential to explore and develop additional and new approaches for conserving and recovering our fossil fuel base. The utilization of microorganisms for specific bioconversion processes are amply documented. The degradation of paraffinic and aromatic hydrocarbons, the removal of complex detergents, waste management, antibiotic production, fermentations of varied types all represent examples of microbial processes that play a crucial role in today’s society. Therefore it is recommended to:

1. Generate a better understanding of the ind genous microflora in petroleum deposits.

Scant knowledge exists concerning the microflora of existing petroleum deposits. The presence or absence of specific microorganisms in non-producing wells may contribute directly to the secondary recovery of petroleum.

2. Analyze for those microbial systems which effect changes in petroliferous deposits.

Development of a more comprehensive picture of the biochemical action of microorganisms against a broader assay of complex petroleum constituents may aid in the development of more efficacious recovery technologies.

3. Assess the chemical and physical nature of reservoir rock to allow for the selection of specific microorganisms that would provide greater opportunities for enhanced secondary recovery of petroleum.

4. Develop a screening program for microorganisms to establish a range and capability profile for hydrocarbon production.

5. Initiate genetic engineering principles into the development of microorganisms for enhanced petroleum recovery and/or production.

6. Develop further the in situ fermentation technology for formation of CO2, H2, CH4 and other byproducts that can aid in secondary oil recovery.

7. Develop specific microorganisms capable of effecting the desulfurization of petroleum as well as removing noxious sulfur components.

8. Organize an international committee to coordinate and collate research efforts as related to petroleum microbiology.

9. Establish an international culture collection for microorganisms that have application to petroleum and/or petroleum products.

10. Develop specific knowledge into the direct effects of microorganisms on oil for enhanced recovery through:

(a) The reduction of interfacial tension and viscosity through microorganisms.

(b) The microbial sequestering of petroleum.

(c) The reduction of surface tension by biosurfactants produced through microbial activity.

(d) The multistep microbial alteration of residual oil to useful secondary products or gases.

11. Develop further knowledge into the application of microorganisms for secondary oil recovery through alteration of the aqueous phase in situ.

(a) The production of microbial-produced water-soluble polymers.

(b) The microbiological treatment of low-quality water for injection purposes.

12. Develop further insight into the microbial alteration of rock structures for release of oil through:

(a) Alteration of the permeability of rock through specific microbial agents.

(b) Surface pile and in situ leaching of rock by specific microorganisms.

(c) Microbiological alteration of keragen and/or keragen-like material.

(d) Simultaneous minerals extraction by microorganisms.

13. Develop microbial processes for recovery of gas through:

(a) Microbial alteration of tight formations such as tight sandstone.

(b) Secondary recovery of residual gas deposits through microbial conversion to secondary and tertiary products.

14. Safety improvement through microbiological action should be explored for development of the removal of methane from underground mines and H2S in certain oil fields.

15. Studies should be directed to those microbial processes which are deleterious to oil recovery such as bio-corrosion, well plugging, etc.

16. Environment. The use of microorganisms should be further developed and extended for the removal of petroleum pollutants from the environment.

The above recommendations are those that can be visualized within 10 years provided that finances and facilities are made available.

Presently, petroleum microbiologists are few in number and not well organized. Accordingly, the principal task is a structuring of the discipline of petroleum microbiology. A step forward would be the establishment of an international microbiological centre as recommended above. Such a centre would provide a focal point for the organization, coordination and cooperation of the research being done by the few petroleum microbiologists throughout the world. It is for these reasons that the conferees recommend governments and private institutions to note, accept, and act on these recommendations.

WORKING GROUP VI

Prices of important substrates and economics of chemical interconversions

Publisher Summary

This chapter discusses the prices of important substrates and economics of chemical interconversions. The important substrates for fermentation processes can be classified into two categories, namely, carbohydrates and hydrocarbons and related compounds. A distinction is made between primary carbohydrates such as starches and sugars and secondary carbohydrates that are byproducts or waste-products that are often derived from a process that involved these primary products. The prices of primary carbohydrates are well-known, and at present, those prices are relatively low. However, the price structure of secondary carbohydrates is often not as well defined. Although the molasses is a secondary carbohydrate, it has a well-defined price structure and, therefore, could be considered as a primary carbohydrate. The carbohydrate wastes such as those from brewing–distilling, canning, cheese making, and meat packing processes could be economic substrates for fermentation both in the developed and in the developing countries. This is because these carbohydrate wastes cannot be discharged to waterways without further treatment to reduce their effluent content. As a result, the economic viability of fermenting these wastes should be compared with the alternative costs of treating these wastes in a sewage plant.

Important substrates for fermentation processes can be classified into:

(a) Carbohydrates

(b) Hydrocarbons and related compounds.

A distinction should be made between primary carbohydrates such as starches and sugars and secondary carbohydrates which are byproducts or waste-products often derived from a process that involved these primary products. With regard to hydrocarbons, there is no similar distinction between primary and byproducts. In Table I these products are listed.

Table I

*either from starch or from cellulose by enzymatic hydrolysis

1. Prices of primary carbohydrates are well-known and at present those prices are relatively low.

The price structure of secondary carbohydrates is often not as well defined. It should be noted that molasses although a secondary carbohydrate has a well defined price structure, and from that point of view could be considered as a primary carbohydrate. On the other hand, the price structure of carbohydrate-containing wastes is not well defined. Often those costs are close to zero provided that wastes are collected from the production plant.

2. The substrates listed in Table I can serve as fermentation media to produce the following products:

(a) Basic chemicals (chemical building blocks) e.g. ethanol, acetic acid, butanol.

(b) Sophisticated chemicals, e.g. steroids, antibiotics, citric acid.

Most of the basic chemicals can be produced more efficiently by chemical processes (involving high temperatures and pressures) using petrochemicals as raw materials. For many sophisticated chemicals, however, fermentation is the only feasible process route, and no competitive chemical process exists.

3. The developed countries of Western Europe and North America have a highly protected agriculture and hence the price of carbohydrate substrates produced in these countries such as starch and sugars is far higher than the world market prices. In these countries, it is, therefore, not feasible to produce basic chemicals by fermentation using the expensive substrates. However, the fermentation route to sophisticated chemicals is quite feasible in these countries because the endproduct has a very high added value.

4. In many countries of the third world there are available relatively large quantities of primary carbohydrates at reasonably low price. We consider therefore that the production of basic chemicals by fermentation of primary carbohydrates could be justified economically in these countries, particularly as an alternative to chemical processes based on high-price petroleum feedstocks.

5. With regard to hydrocarbon substrates we consider that these will become of significance as fermentation media to produce single cell protein particularly in Europe.

Their importance in single cell protein production is due to the fact that these substrates are pure and available in large quantities which makes it possible for manufacturers to produce very large quantities (i.e. 100,000 tons/year) of single cell protein in one plant.

In view of the fact that all of Europe’s requirements for feed protein are imported, single cell protein could help to make Europe more self-sufficient.

Another important area for hydrocarbon substrates is in the production of various sophisticated chemicals such as citric acid or lysine. The advantage in using hydrocarbon substrates is in the fact that smaller quantities of waste are produced at the end of a hydrocarbon fermentation as compared with waste produced using carbohydrate substrates.

6. Carbohydrate wastes (e.g. from brewing-distilling, canning, cheese-making and meat packing processes could be economic substrates for fermentation both in the developed and in the developing countries. This is due to the fact that these carbohydrate wastes cannot be discharged to waterways without further treatment to reduce their effluent content. Hence the economic viability of fermenting these wastes must be compared with the alternative costs of treating these wastes in a sewage plant.

In most cases, we consider that fermentation processes using carbohydrate wastes can produce a range of products such as yeast (proteins), organic acids or vitamins which can generally be sold as an animal feed supplement on the open market. This in many cases is cheaper than treating the waste in a sewage plant before discharging to the water-ways.

7. Substrates for fermentation must be considered in the same way as raw materials for chemical processes. Like raw materials the substrates usually have a well-defined price structure which can vary from country to country depending on the market situation, governmental pricing policy etc.

Although the price structure of carbohydrate waste is not as clearly defined as the price of primary carbohydrates or hydrocarbons, the economics of fermenting carbohydrate wastes must be established in every case by comparison with the alternative which involved treatment of the waste in a sewage plant.

We therefore consider that the substrates, which we have described are all economically feasible for various types of fermentation processes.

WORKING GROUP I

Assistants: I. Probst and J. Wiegel - Göttingen

WORKING GROUP II

Assistants: R. Conrad and E. Siefert - Göttingen

WORKING GROUP III

Assistants: H. Hippe and S. Schoberth - Göttingen

WORKING GROUP IV

Assistants: K. Schneider and F. Widdel - Göttingen

WORKING GROUP V